Open Radio equipment Interface

Mobile operators typically deploy a base station architecture with functions distributed into 2 network elements: a BaseBand Unit (BBU) which performs the processing of the radio protocols (physical layer and higher layers), and the Remote Radio Head (RRH) or Integrated Active Antenna, which converts the digital baseband signal into the analogue signal for transmission/reception over the air.

A Remote Radio Head is typically placed on the antenna mast (or even integrated with the antenna itself) to reduce power losses in the cabling between RRH and antenna. The BBU is typically placed in a more convenient location to allow easy access by the operator. The RRH is connected to the BBU over a digital link. This Base Station architecture aims to improve the energy efficiency of the Base Station.

The interface between the BBU and RRH can currently be provided in a "semi proprietary" nature, e.g. based on industry standards like CPRI (Common Public Radio Interface) or OBSAI (Open Base Station Architecture Initiative). However, mobile operators and other industry players saw a need to have greater flexibility and choice of BBU and RRH equipment suppliers, to allow maximum opportunity for operator Base Station product requirements to be met, especially considering aspects such as:

End customer experience

Energy consumption

RRH form factor and integrated (active) antenna solutions

The above aspects become more complex for operators to manage as more radio access technologies and frequency bands are deployed at the same radio site, and also as different Base Station deployment types and more centralized BBU (otherwise known as "C-RAN") deployments are considered.

An open standardized interface between BBU and RRH aims to enable this greater BBU and RRH supplier flexibility.

ETSI had established the Open Radio equipment Interface Industry Specification Group (ORI ISG) to develop an interface specification enabling interoperability between Base Band Units (BBUs), more generically defined as 'Radio Equipment Controllers' (RECs), and Remote Radio Heads (RRHs) more generically defined as 'Radio Equipment' (RE), of base transceiver stations of cellular mobile network equipment. The group was closed in July 2016. ORI ISG deliverables will be maintained by the ETSI Technical Body RRS accessible via the ETSI Portal.

The ETSI ORI Industry Specification Group was a direct result of requirements work undertaken by the NGMN Alliance, in their OBRI (Open BBU RRH Interface) project. The ISG was strongly supported by the NGMN Alliance, and leading mobile network operators and telecommunication equipment vendors are among the ISG's founding members.

The ORI interface was built on top of the interface already defined by the CPRI (Common Public Radio Interface) group. However, options were removed and functions were added with the objective of making the interface fully interoperable.

The first release of the ORI interface, published in 2012, provided a digitized radio base station interface enabling single-hop topologies. Different information flows (User Plane data, Control and Management Plane data, and Synchronization Plane data) were multiplexed over the interface. ORI covers OSI protocol layer 1, Layer 2 up to Layer 7 and is based on CPRI version 4.1. ORI Release 1 provided support for UMTS, LTE and LTE-Advanced technologies.

ORI Release 2 added support for multi-hop topologies and RRU chaining, as well as 9.83 Gbit/s line bit rate, and is based upon CPRI version 4.2.

ORI Release 3 extended support to GSM technology and was based on CPRI version 5.0.

ORI Release 4, published in October 2014, was based on CPRI version 6.0. Release 4 adds IQ data compression for LTE and supports a line bit rate up to 10.14 Gbit/s. This is particularly useful in C-RAN type network topologies.